B. Kusz

Ionic conductivity of bismuth silicate and bismuth germanate glasses

Abstract The results of d.c. and a.c. electrical conductivity measurements in Bi x Ge 1− x O 2−0.5 x (where x =0.13, 0.23, 0.33, 0.47) and Bi x Si 1− x O 2−0.5 x (where x =0.47, 0.57, 0.67) glasses are reported and analysed with the aim of understanding the conduction mechanism. A suggestion is given that the electric conductivity in these glasses can be interpreted by single ionic mechanism. An explanation of a pronounced increase in conductivity for x >0.33 was proposed on the basis of percolation in high mobility BiO 5–6 network.

The electronic conductivity mechanism in Bi-Sr-Ca-Cu-O glass-ceramics

Abstract The results of electrical conductivity measurements in Bi2O3-SrO-CaO-CuO glass-ceramics are reported. It is shown that a sharp increase in the conductivity observed at 460°C is attributed to the crystallization of the Bi2Sr2CuO6 (Bi-2201) superconducting phase in the glass matrix. The mechanism of electrical conductivity in this glass-ceramic can be explained as a result of discontinuous metallic structures of the Bi-2201 phase which appear in the glass matrix during annealing. The low-temperature conductivity obeys the law [sgrave](T) = [sgrave]0exp[(-T 0 /T)n] with n changing from 1/4 to 1/2 with decrease in the temperature. This cross-over is related to a granular structure in which a parabolic Coulomb gap exists in the density of states N(E) near E F. We also show that the superconductivity effect should be taken into account for T−1/2 conductivity behaviour. It is shown that the Bi-Sr-Ca-Cu-O glass after a very short heat treatment at 820°C exhibits the superconducting transition. In the normal state the conductivity is typical for granular metals and the activation energy continuously decreases with decreasing temperature.

Internal friction in high Tc iron doped 1-2-3 yttrium ceramic superconductors

Abstract The internal friction, Youngs modulus and shielding effect in yttrium ceramics doped with various amounts of iron have been measured in the temperature range 20 – 160 K. There exist several internal friction peaks, some of them common for all specimens. Only one, around 100 K, might be inexplicitly associated with the superconducting properties. No anomaly in the internal friction has been found at the transition temperature.

Internal friction in ErBa2Cu3Ox superconductors

Abstract The internal friction ( Q −1 ) spectrum of ErBa 2 Cu 3 O x superconducting ceramics has been measured at two different frequencies (approx. 6 Hz and 250 Hz). Several subsequent cycles of simultaneous measurements of internal friction, elasticity modulus and resistivity were performed. An evolution of the internal friction during subsequent measurements and ageing in vacuum and oxygen has been observed.

Low-temperature mechanical energy dissipation phenomena in lanthanum superconductors

Abstract The anelastic properties of ceramics which belong to the lanthanum family of superconductors were studied. The internal friction and Youngs modulus measurements were carried out by the vibrating reed technique in the temperature range from 20 to 300 K. The measurement frequency was in the range of 90–760 Hz. A large internal friction, corresponding to a maximum of the relaxation, was observed at a temperature about 50–60 K. An interesting correlation of both the peak height and the relaxation strength with the dopant content x has been found. An electronic relaxation phenomenon was considered as a possible source of the low-temperature internal friction maximum. The well known HTT→LTO phase transition was observed through both a pronounced change in Youngs modulus and the internal friction maximum. Also the LTO→LTT phase transition was indirectly observed through an anomalous change in the Youngs modulus.

Anelastic effects in CuO

Abstract The anelastic effects in CuO were measured at the frequency of a few hundred Hz in temperature range 20–300 K. The samples were prepared according to the procedure known for the yttrium ceramic superconductors. The spectra show distinct similarity to those of the yttrium ceramic superconductors. The only noticeable differences are visible in the range near the superconducting transition Tc where two peaks exist in the ceramic superconductor. The outgasing of the CuO sample at temperature of 200 °C reveals the appearance of two new peaks at temperatures 130 K and 155 K. The antiferromagnetic transition at 215 K and an unknown origin phenomena at 35 K were observed which do not depend on the outgasing procedure. The results show that at least some of the properties of the cupric oxide are preserved in the yttrium ceramic superconductors.

Relaxation phenomena in 1-2-3 high Tc superconductors

Measurements of internal friction and ultrasonic wave attenuation by several authors have been compared. The activation energy and relaxation time of four relaxation processes have been determined. A possible interpretation of two processes is suggested.

Growth and characterization of PrBa2Cu3O7-δ single crystals

Abstract We report on the growth of PrBa 2 Cu 3 O 7-δ single crystals in the Al 2 O 3 and ZrO 2 crucibles by flux method. The high influence of the reaction between crucible and liquid on the initial melt composition has been established. We found that the precipitation of the chemically stable compound BaZrO 3 and BaAl 2 O 4 occurs by direct chemical reaction between BaCuO 2 and ZrO 2 or Al 2 O 3 crucibles materials. Free separated crystals with maximum size of 3 x 5 x 0.1 mm 3 have been obtained. PrBa 2 Cu 3 O 7-δ crystals exhibit a typically semiconducting behaviour. The resistivity depends on the thermal treatment and decreases by about two orders of magnitude for oxygen concentration between 6.65 to 6.95.

Some aspects of mechanical energy dissipation phenomena in yttrium superconductors.

The results of measurements of internal friction and Youngs modulus in yttrium 1-2-4 superconducting ceramics are reported. The internal friction maxima observed in the temperature range from 30 K to 100 K are of relaxation nature. The approximate values of activation energy and relaxation time of these phenomena are given. The anelastic properties of the 1-2-4 and 1-2-3 superconductors are compared. An alternative mechanism for one of the relaxation processes is proposed.

Superconducting and anelastic effects in Pb-doped BiSrCaCuO ceramics

Abstract The resistivity, shielding and anelastic effects in Pb-doped Bi 2− x Pb x Sr 2 Ca 2 Cu 3 O y ceramics, where x = 0-0.6, have been studied. The best superconducting properties have been achieved for x = 0.4. The chemical analysis shows that the real Pb content is lower than the nominal. Energy dissipation spectra show no maximum around the transition temperature. A sharp peak at 215 K has been interpreted as being due to a first order antiferromagnetic transition.